[Borgbackup] hash function and collisions?

[Maurice Libes]

hi to all

Just a theoritical question that a friend of mine asked to me :-)

I am not a mathematician and I dont know what to answer about the hash 
function and collision probability

If I understand, in order to store the chunks and to reference them, a 
hash value is computed on the chunk data, with a hmac-sha256 function ?

I read somewhere that the probability of having a collision is something 
less than 2^256 ?

but what if it happens ?
is borg able to detect a possible hash collision ( "n" fragments 
referenced by a same hash value) ?

if not, this would say that we might have 2 differents chunks  
referenced by the same hash value
and so a wrong file in the repository?

sorry if the question makes no sense

thanks for any comment

M


-- 
M. LIBES
Service Informatique OSU Pytheas - UMS 3470 CNRS
Batiment Oceanomed
Campus de Luminy
13288 Marseille cedex 9
Tel: 04860 90529


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